Quite good film on the Talking Pictures channel this evening, a black and white British film called "Tiger in the Smoke" (1956). I saw it on television many years ago and thought it quite interesting. It's based on the novel by Margery Allingham, the detective story writer. The book is one of her Albert Campion books but in the film, he is not in it.
The film ise set in a noirish smog-shrouded London - the smog is quite effective.
Not to be confused with "Footsteps in the Fog", the Stewart Granger/Jean Simmons film.